UV coordinates are locked from -10 to 10?
In code most UI widgets such as sliders, number fields etc ask you to set min and max values.
In some cases this can be relevant to how the widget behaves (for example, sliders with large ranges are harder to slide to specific value due to display precision).
In this case the limits are most likely arbitrary.

For things like texture looping or tiling, normally this is done by using the vector mapping node in the materials edit to scale the UV coordinates, rather than in the original coordinates.